Friday, June 17, 2011

The New Scientist has an article on more evidence that modern Homo sapiens and archaic Homo sapiens may have interbred and that this interbreeding may have helped modern humans increase their colonization of the planet. The article, by Michael Marshall, has this to say:

[Peter Parham] focused on human leukocyte antigens (HLAs), a family of about 200 genes that is essential to our immune system. It also contains some of the most variable human genes: hundreds of versions - or alleles - exist of each gene in the population, allowing our bodies to react to a huge number of disease-causing agents and adapt to new ones.

The humans that left Africa probably carried only a limited number of HLA alleles as they likely travelled in small groups. Worse, their HLAs would have been adapted to African diseases. When Parham compared the HLA genes of people from different regions of the world with the Neanderthal and Denisovan HLAs, he found evidence that non-African humans picked up new alleles from the hominins they interbred with.

As I mentioned in another post, it is not clear just how “specific” the Denisovans really are. Parham's work shores up the work by Svante Paabo earlier that suggests that Neandertal DNA makes up between 4 and 6 % of modern DNA, a finding that can only occur within the context of hybridization on some level. It also vindicates the work in Lagar Velho, which indicated the presence of a Neandertal/early modern hybrid grave. The weight of evidence is slowly shifting away from the straight “out-of-Africa,” replacement model that has been so dominant for the last few decades.